Research Into The Dynamic Respose Of Loess Shallow Tunnel Undercrossing Railway Station

With the rapid development of urban rail transit,urban subways are accelerating construction.The construction of metro tunnels is affected by surface locomotive loads,which can not guarantee the safety construction of tunnels under tunnels and the safe operation of railways.At present,there are few researches on the dynamic loads of locomotives during tunnel construction in loess areas.Therefore,based on the engineering background of the subway line 4 passing through Xi’an railway station and the theory of dynamics,the field vehicle test and ABAQUS finite element software were used to analyze the propagation law of locomotive vibration in the loess layer and the dynamic effect of the tunnel under the shallow tunnel.The main research results obtained are as follows:(1)In order to explore the law of vibration response of each object under the project,a live vibration test method was used to test the locomotive stocks,the loess layer and the tunnel underneath.The results of the locomotive stocks test show that the amplitude of vibration acceleration at the joints of rails is larger than that at the seamless joints and turnouts of the rails,and the amplitude at the turnouts is the next;the formation test results show that the amplitude of vibration acceleration decreases as the depth of the formation increases.However,due to the use of a full-section grouting technique in the tunnel underneath,soil layers below 4.2 m in depth are disturbed and a rebound in the acceleration amplitude occurs.The results of the tunnel test show that when the train passes directly above the tunnel,the lining structure has the greatest vibration response.(2)The modified wheel-rail model was introduced into the test analysis method to obtain the dynamic load of the locomotive and applied it to the 3-D numerical model to analyze the influence of the construction of the subway tunnel on the locomotivevibration attenuation rule and predict the dynamic response of the entire track-subgrade-tunnel system after the train was opened to traffic.The dynamic analysis shows that there is a local amplification effect of the dynamic effect when there is a tunnel below the railway subgrade.When the locomotive and the subway train are traveling at the same time,the vibration attenuation law within 4m of the stratum depth is dominated by the locomotive load,and the subway train load is less than 4m.(3)A three-dimensional numerical model was established to consider the influence of locomotive running speed,driving mode,lining parameters,and locomotive strand type on the dynamic response of the lining structure of an underpassed shallow tunnel.The dynamic analysis shows that when the single-row locomotive running speed is 90km/h,the vibration response of the underpass tunnel is the largest;when the double-row locomotive runs at the speed of 90km/h in the same direction,the vibration response of the tunnel under the tunnel is largest,and the vibration speed and motion The amplitude of the displacement is close to the norm;the reinforcement of the initial lining concrete has little effect on the vibration response,but the increase of the initial lining thickness can weaken the dynamic effect of the upper locomotive;when the locomotive passes through different types of gangways,the dynamic response of the tunnel under the tunnel preserves the original waveform features.